(a) Field of the Invention
The present invention concerns processing of filament yarns, and more particularly it pertains to a method and an apparatus for performing false-twisting of filament yarns to produce crimped filament yarns.
(b) Description of the Prior Art
Conventional false-twisting methods may be divided roughly into the following two types, one of which is the so-called spindle system and the other may be termed as the friction system.
As is discussed in my U.S. Pat. No. 4,047,373 specification in detail, the known spindle system is such that the processing speed, as measured in terms of the running speed of the filament yarn, is limited to 100 m/min..about.150 m/min. at the most. Above this level, the filament yarns which are subjected to a false-twisting process tend to develop a number of hair or fluffs and breakage of filament yarns resulting in rejectable yarns. Also, in this spindle system, it is mandatory that the pull-out tension of the filament yarn has to be greater than the tension of the filament yarn located on the twisting zone. In order to raise productivity, the spindle which is required one for each filament yarn has to be rotated at a ultra-high speed and also the pull-out tension is required to be increased. However, with an increase in the pull-out tension which is applied to the filament yarn to be processed, there suddenly arises an increase in the number of development of hair or fluffs in the filament yarns and the number of broken yarns, so that no crimped filament yarns of the desired good quality can be obtained.
The false-twisting method of the friction type mentioned above typically employs a pair of mating rotatable frictional members such as two belts or frictionally engaging rotary rigid disks or conically-shaped rotary members having spiral row of ridges formed on their surfaces. The working surfaces of these frictional members have a large friction coefficient. A filament yarn is fed between the work surfaces of the mating running frictional members for contact therewith to be twisted thereby. While the false-twisting system relying on the surface friction of the working members allows a higher processing rate over the spindle system, the former system is accompanied by the problem that there easily develops fluffs and breakage of filament yarns with an increase in the speed of processing. Furthermore, in this friction system, the filament yarn is twisted as it is being contacted with the frictional work surfaces of the running members, and accordingly this system is poor in the processing efficiency such that there easily develops "stick slip" between the filament yarn and the high friction members, resulting in the development of portions of uneven twists which, in turn, tend to cause non-twisted portions remaining in the crimped filament yarns produced.
Moreover, in such known false-twisting systems, the number of twists or turns imparted to the filament yarn is recognized either by sampling the running filament yarn and by measuring the number of the actual turns thereof or by just an inference alleging from the tension applied to the filament yarn being twisted while giving reference to the predetermined mutual relationship between the actual turns and the tension applied onto the filament yarn at the time of twisting. Thus, in the prior art, it is difficult to make accurate control of the number of turns imparted to the filament yarns being processed.